Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$123.39	10.330%	$136.1362	$136.14	$136.15	$136.10
Purchase #2	$123.55	3.629%	$128.0336	$128.03	$128.05	$128.00
Purchase #3	$78.76	13.324%	$89.254	$89.25	$89.25	$89.30
Purchase #4	$197.41	9.537%	$216.237	$216.24	$216.25	$216.20
Purchase #5	$143.79	3.492%	$148.8111	$148.81	$148.80	$148.80
Purchase #6	$90.83	6.347%	$96.595	$96.60	$96.60	$96.60
Purchase #7	$139.82	3.275%	$144.3991	$144.40	$144.40	$144.40
7 purchase totals =	$897.55		$959.4660	$959.47	$959.50	$959.40